The bathymetry and sediment distribution of Barkley Sound and the adjacent continental shelf off the west coast of Vancouver Island have been markedly affected by the late Pleistocene glaciation and modern sedimentary processes. Several fjords widen and coalesce to form the sound, which is continuous with glacially eroded basins on the inner continental shelf. These basins are flanked by flat-topped banks, the larger of which merge with the outer shelf—a gently sloping plain that terminates at the 200 m isobath, 58 km from shore.Modern sediments are restricted mainly to Barkley Sound where the glaciated "basin and sill" bathymetry and an estuarine circulatory system prevent the predominantly muddy detritus from reaching the continental shelf. Relict sands and gravels cover most of the shelf except within basins and drowned river valleys where muds prevail. This relict cover was initially dispersed by glaciers and meltwater streams, then later inundated during the Holocene Transgression, and is now being partly reworked by the present hydraulic regime. Near the shelf-break relict sediments are sparse and authigenic sands (glaucontized mudstone pellets) predominate together with residual sediments derived from submarine exposures of Tertiary mudstone.

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